1. Field of the Invention
The present invention relates to an electrical junction box such as a junction box and a relay box which are used for electrical wiring, for example, of an automotive vehicle. The present invention relates particularly to an electrical junction box having a construction which allows an easy combining work of a lower cover, a wiring sheet, etc. thereof.
2. Related Art
Referring to FIG. 9, a conventional junction box X or a conventional electrical junction box such as a relay box and components including a distributing board 4 of the box will be briefly discussed hereinafter.
FIG. 9 is an exploded perspective view of the conventional electrical junction box X which comprises an upper cover 1, a distributing board 4, a wiring sheet 6, routing conductors 9 and a lower cover 10. The electrical junction box X has a junction box main body consisting of the upper cover 1 and the lower cover 10 which are made of a synthetic resin material. The junction box main body accommodates the distributing board 4 consisting of busbars, a circuit board, etc. Terminals constituted by the busbars are disposed in a connector provided on the upper cover. The electrical junction box X shown in FIG. 9 may be called as a busbar assembly including the distributing board 4 and the wiring sheet 6.
The upper cover 1 has a mini fuse accommodation section, a connector housing, etc. and also protects internal components including the distributing board, the busbars, and terminals, for example, female terminals for mini fuses. The upper cover 1 is a main cover. Alternatively, the lower cover may be a main cover in accordance with applications and operational conditions thereof.
The lower cover 10 has a mini fuse accommodation section, a connector housing, etc. and also protects internal components including the distributing board, the busbars, and terminals, for example, female terminals for mini fuses. Generally, the lower cover is combined to the upper cover 1 to define the electrical junction box X. The lower cover 10 is also called as an underside cover.
These female terminals will be discussed herein. The female terminal has each end provided with a receptacle-type connection portion, for example, which is called as a fuse Fxe2x80x94F terminal when it connects a busbar with a fuse and as a relay Fxe2x80x94F terminal when it connects a busbar with a relay. Fxe2x80x94F shows two female-type contacts.
Such junction boxes, junction blocks, or electrical junction boxes X like a relay box include integrated block components defined by combining a plurality of connectors, relays, and fuses into an electrical circuit having electrical wires, busbars, and etc. Generally, such boxes are utilized to divide a wiring harness. The distributing board 4 is an insulating plate which can retain busbars and electrical wires. The busbar is made of a conductivity metal plate and has a lot of electrical contacts to divide an electrical circuit into a plurality of circuits.
As illustrated in FIG. 9, the lower cover 10 has a bottom wall provided with a through-hole portion 8c having an alignment enhancing through-hole 8a. The alignment enhancing through-hole 8a is slightly apart inside from a side wall of the lower cover 10. The distributing board 4 consists of a distributing board 4a disposed on the upper cover 1 and a distributing board 4b disposed in a side of the wiring sheet 6. On an underside of the distributing board 4, there is provided a busbar associated with the alignment enhancing through-hole 8a of the lower cover 10.
The wiring sheet 6 is disposed under the distributing board 4. Under the wiring sheet 6, electrical wires 9 having curved portions such as routing conductors are attached to the wiring sheet 6 at predetermined positions. Next, referring to FIG. 10, a step for inserting the busbar into the alignment enhancing through-hole 8a of the through-hole portion 8c formed in the lower cover 10 will be discussed.
FIG. 10 is an enlarged longitudinal sectional view of the conventional alignment enhancing through-hole 8a and a surrounding part thereof and shows a busbar 5, particularly a terminal portion 5xe2x80x2 of a connector busbar 5c. The connector busbar 5c has a tab tip portion 5b allowing an easy insertion of the busbar 5 into the alignment enhancing through-hole 8a. 
The lower cover 10 is constituted by a bottom wall 10a and side walls 10b, and the bottom wall 10a is compensated by ribs 10k. The bottom wall 10a is formed with the through-hole portion 8c having the alignment enhancing through-hole 8a. 
The alignment enhancing through-hole 8a formed in the lower cover 10 has an upper insertion opening 8f and an intermediate tapered portion 8e for an easy insertion of the connector busbar 5c into the alignment enhancing through-hole 8a. The alignment enhancing through-hole 8a has a lower exit opening 8g for extending the busbar 5 therefrom. Below the alignment enhancing through-hole 8a, that is, under the lower cover 10, there is provided a connector housing 8. The distributing board 4, the wiring sheet 6 having the routing conductors 9, and the lower cover 10, which are illustrated in FIG. 9, are combined with each other, so that the connector busbar 5c shown in FIG. 10 is inserted into the alignment enhancing through-hole 8a to pass through the alignment enhancing through-hole 8a so as to extend toward the connector housing 8. This defines a male connector which is connected to another electrical component such as a wiring harness having a receptacle connector.
FIG. 11 is a bottom view showing a wiring area A and a neighboring area thereof in respect of the conventional wiring sheet 6 of the distributing board. The bottom view is a general illustration of the wiring sheet 6 provided with the routing conductors 9, which is taken upward from the bottom wall of the lower cover 10. The wiring sheet 6 is mounted on the lower cover 10 so as not to interfere with the through-hole portion 8c and the alignment enhancing through-hole 8a of the lower cover 10.
The wiring sheet 6 has a base plate 6a on which a lot of the routing conductors 9 are mounted. The routing conductors 9 are arranged in the wiring area A so as to have adequate curved portions. The routing conductors 9 are electrically connected in a pattern by a predetermined large number of press-fit terminals 15 disposed on an underside surface of the distributing board. Further, the base plate 6a of the wiring sheet 6 is formed with a plurality of positioning holes 6c for accurately combining the wiring sheet 6 with the upper cover 1, the lower cover 10 having the side wall 10b, and the distributing board 4.
Referring to a prior art, Japanese Utility Model No. 3-40048 discloses an electrical junction box used for connection of wiring harnesses. The electrical junction box accommodates a busbar wiring pattern having tab terminals which are accurately vertically extended to achieve an improved connection with an associated connector.
Generally, the busbar terminals attached on the distributing board are not accurately oriented with variations in orientation thereof. Thus, the insertion opening 8f of the alignment enhancing 8a (FIGS. 9 and 10) of the lower cover 10 must have a larger size so that the terminal 5xe2x80x2 of the busbar 5 ununiformly attached in the distributing board 4 may be easily insertable into the alignment enhancing through-hole 8a of the lower cover 10 as illustrated in FIG. 10.
However, the alignment enhancing through-hole 8a shown in FIG. 10 must have the tapered portion 8e of a comparatively longer length because of an easy insertion of the terminal 5xe2x80x2 of the connector busbar 5c, resulted in a larger size of the through-hole portion 8c. As illustrated in FIG. 10, The through-hole portion 8cincluding the alignment enhancing through-hole 8a is higher than the side wall 10b above the bottom wall 10a of the lower cover 10.
This is caused by the larger size of the insertion opening 8f of the alignment enhancing through-hole 8a to receive the busbar 5. The elongated tapered portion 8e of the alignment enhancing through-hole 8a allows the larger size of the insertion opening 8f of the alignment enhancing through-hole 8a to receive the busbar 5. Therefore, the required length of the alignment enhancing through-hole 8a causes the through-hole portion 8c to be higher than the other part above the lower cover 10.
The conventional lower cover 10 of such construction is not suitable for size minimization of the electrical junction box X. A molding die for the lower cover 10 tends to be expensive since the molding die may have a larger size so as to form the extended portion of the through-hole portion 8c. 
Furthermore, as illustrated in FIG. 11, the conventional wiring sheet 6 provides the wiring area A which is reduced in size. Referring to details, the conventional wiring sheet 6 is defined not to interfere with the through-hole portion 8c and the alignment enhancing through-hole 8a of the lower cover 10. This reduces the wiring sheet 6 in size, so that the wiring sheet 6 having the wiring reduced area A is undesirably used for the electrical junction box X.
As mentioned above, the electrical junction box X needs to keep the necessary wiring area A of the wiring sheet 6 and another area for the through-hole portion 8c and the alignment enhancing through-hole 8a of the lower cover 10. This configuration is not preferable for reduction in size and weight of the electrical junction box X.
An object of the present invention is to provide an electrical junction box which allows an easy combining work of a distributing board, a wiring sheet, and a lower cover in addition to achieving a smaller assembling tolerance thereof. Another object of the present invention is to provide a larger wiring area of the wiring sheet to arrange routing conductors thereon. Additionally, the present invention aims size minimization of the wiring sheet, the lower cover, and molding dies thereof, which also achieves simplification of the molding dies and smaller material costs of the wiring sheet and the lower cover.
For achieving the objects, an aspect of the invention is an electrical junction box having an upper cover, a distributing board provided with a busbar, a wiring sheet, and a lower cover formed with a through-hole for receiving terminal of the busbar, characterized in that the wiring sheet is formed with a through-hole for receiving the terminal of the busbars whereby the terminal of the busbar is inserted into the through-hole of the lower cover with a smaller assembling tolerance when the lower cover is combined with the wiring sheet which preliminary combined with the distributing board.
This configuration, unlike the above-mentioned conventional electrical junction box, does not need to have a larger insertion opening formed in the lower cover for the busbar terminal with keeping a predetermined insertion distance. Because, the distributing board cab be preliminary combined with the wiring sheet before combined with the lower cover so that an insertion tolerance of the busbar terminal into the through-hole may be smaller. In addition, the through-hole of the lower cover may have a shorter insertion length. This enables a size minimization and a weight reduction of the lower cover and a cost reduction of molding dies for forming the. lower cover.
More specifically speaking, in the conventional, the wiring sheet has no through-hole and only the lower cover has the through-hole. Thus, the through-hole of the lower cover is defined to allow the position variations of the busbar terminal of the distributing board. Since the wiring sheet is disposed between the distributing board and the lower cover, it is necessary to consider a total assembling tolerance of the wiring sheet, the distributing board provided with each busbar, and the lower cover.
The busbar terminals attached to the distributing board are not accurately arranged in the distributing board but have often variations in position thereof. This requires a larger insertion opening of the through-hole of the lower cover to allow an easy insertion of the busbar terminal of the distributing board into the lower cover through-hole regardless of the position variations of the busbar terminal.
However, in order to accurately position the busbar terminal in the through-hole of the lower cover, the through-hole needs to have the tapered portion extending from the insertion opening to the exit opening thereof in addition to the larger insertion opening. The tapered portion causes the through-hole to be progressively smaller in section. Therefore, a smaller assembling tolerance of the busbar terminal increases the length of the through-hole portion.
Meanwhile, in the present invention, the wiring sheet is formed with the through-hole through which the busbar is inserted and the distributing board is combined with the wiring sheet. The combined distributing board having the busbar is combined with the lower cover to define the electrical junction box. Thereby, an assembling tolerance of the busbar in the electrical junction box can be divided into one between the distributing board and the wiring sheet through-hole and another between the wiring sheet through-hole and the lower cover through-hole.
The busbar terminal disposed in the distributing board is corrected in its position due to insertion into the wiring sheet through-hole to reduce position variation of the busbar terminal when the distributing board is combined with the wiring sheet. This reduces the through-hole of the lower cover and its associated construction in size.
Furthermore, such combination of the wiring sheet and the distributing board allows the wiring sheet through-hole to guide the busbar terminal attached to the distributing board, reducing a lateral deviation of the busbar tab. The combined unit of the distributing board and the wiring sheet is easily combined with the lower cover, enabling a speedy and effective assembling work of the electrical junction box.
Preferably, the through-hole formed in the wiring sheet has an insertion opening, an exit opening, and a tapered portion such that the through-hole has a sectional area progressively smaller from the insertion opening to the exit opening, and the exit opening has a width substantially equal to a thickness of the terminal of the busbar.
Such configuration allows the busbar attached to the distributing board to be easily inserted into the through-hole of the wiring sheet and to be inserted into the lower cover through the wiring sheet to define the connector with a smaller assembling tolerance between the busbar and its received portion.
In order to insert an inaccurately positioned busbar of the distributing board into the through-hole of the wiring sheet, the insertion opening of the through-hole shall be increased in width. However, since it is necessary to accurately position the busbar within the through-hole, the size of the exit opening is determined to be approximately equal to the thickness of the busbar terminal. Furthermore, the tapered portion is provided to extend from the insertion opening to the exit opening of the through-hole, so that the busbar terminal passes smoothly the through-hole of the wiring sheet.
Preferably, the through-hole of the lower cover has an extending length substantially equal to a bottom wall thickness of the lower cover.
Such configuration allows minimization of the through-hole and its associated surrounding portion of the lower cover as well as an accurate positioning of the busbar terminal. This reduces the lower cover in size, enabling minimization of molding dies of the lower cover together with a cost reduction of the molding dies.
In this configuration, the wiring sheet is formed with the through-hole so that a smaller assembling tolerance for insertion of the busbar terminal can be provided between the busbar terminal attached to the distributing board and the through-hole of the lower cover. This allows a smaller deviation of the busbar tab when the distributing board combined with the wiring sheet is combined with the lower cover. Additionally, a smaller assembling tolerance between the distributing board combined with the wiring sheet and the lower cover can be provided, allowing minimization of the through-hole and its associated surrounding portion of the lower cover.
Preferably, the electrical junction box has a connector housing positioned under the lower cover, the connector housing associated with the through-hole of the lower cover.
Such configuration of the busbar terminal and the connector housing defines the male connector which can be electrically connected to an associated receptacle connector. Thus, the electrical junction box according to the present invention can be electrically connected to another electrical component with ease.
Preferably, the through-hole of the wiring sheet is positioned in a wiring area of the wiring sheet.
Such configuration allows the wiring sheet to efficiently arrange the routing conductors and the through-hole thereon without any restriction of the base plate of the wiring sheet. Thus, the base plate of the wiring sheet can provide an effective arrangement area, reducing the electrical junction box in size and weight.